Fertilization effects on changes in soil flux and organic C in switchgrass (Panicum virgatum L.) land managed for biomass production were investigated. The mean daily soil flux in the manure treatment was 5.63 g , and this was significantly higher than the mean value of 3.36 g in the control. The mean daily fluxes in N and P fertilizer treatments plots were not different when compared to the value in the control plots. Potentially mineralizable C (PMC), soil microbial biomass C (SMBC), and particulate organic C (POC) were highest at the 0 to 10 cm depth of the manure treatment. Potentially mineralizable C had the strongest correlation with SMBC (r = 0.91) and POC (r = 0.84). There was also a strong correlation between SMBC and POC (r = 0.90). Our results indicated that for the N and P levels studied, fertilization had no impact on temporal changes in soil organic C, but manure application had a significant impact on temporal changes in soil evolution and active C constituents such as PMC, SMBC, and POC.